1. Field of the Invention
The present invention relates to a semiconductor printing apparatus, that is, apparatus for transferring a pattern of a photo mask onto a wafer in the manufacturing process of semiconductors.
2. Description of the Prior Art
In the process for manufacturing semiconductors, in general, many repeated times of mask processing are required. During these processings, the temperature condition may vary from time to time. Also, characteristics of the transfer optical system may vary. Under these conditions, the photo mask and wafer have some difference in elongation or they are subjected to some relative deformation. Further, the aligned relation between mask and wafer is affected by intermediate processings such as etching. All of these variations of parameters together cause some deviation of the pattern.
If exposure is carried out with such deviated pattern, then it is no longer possible to make regular semiconductors. Therefore it is necessary to prevent or compensate for the algnment error of the pattern between the mask and wafer despite such parameter variation.
As a solution to the above problem, such apparatus has been known in which temperature-controlled air is blown against the mask or wafer (cf. U.S. Pat. No. 4,202,623 and Japanese Utility Patent Application laid open No. 17,951/1981). The blow air is pre-controlled to a constant temperature intending to keep constant the temperature of the mask or wafer or the temperature difference between mask and wafer. However, it is impossible to control the temperature of plural different sections respectively and independently by means of fluid although it may be possible to control the temperature difference as a whole. At present, the pattern used in printing semiconductors is highly miniaturized. Individual alignment of plural different sections can not be attained by the total temperature control by use of fluid as mentioned above.
Japanese Utility Patent Application laid open No. 88,238/1980 has disclosed the use of a plural number of air nozzles in the above-mentioned type of apparatus. However, this means a mere division of blown air by plural nozzles. It is by no means possible to control the temperature of plural different sections individually and independently according to the prior art.
Generally, temperature control by means of fluid involves the following problems:
First, as the heat capacity of a mask and a wafer is larger than that of air, a relatively long time is required to adjust the temperature of the mask or wafer to a determined constant level. Second, the temperature control by blowing air can not follow such a rapid change of temperature of the mask or wafer as is caused by a disturbance. Third, although the blown air itself is an air-controlled clean gas, there is a possibility that dust and foreign particles may be caught in the stream of blown air by convection of the blown air. Last, the refractive index of the air in the optical path may be varied from time to time by any disturbance caused by the air blown, which in turn may cause fluctuation of the projected optical image.
For the reasons mentioned above it is objectable to use the prior art technique in alignment of a miniature pattern.